1. Field of the Invention
This invention relates to impact printers. More specifically, it relates to a ribbon cartridge for impact printers.
2. Description of the Prior Art
With the development of the impact printer field in the direction of high speed printers producing high quality printing suitable for correspondence at speeds in the order of 60 cycles per second, new needs have arisen with respect to printer ribbon structures, cartridges and drive mechanisms.
Because of the high throughput of such impact printer apparatus and the consequently high volume of printed characters, the art has had to provide a ribbon which is relatively low in cost but yet has to provide high quality printing. Because of the difficulty in meeting these requirements with the more traditional fabric base or carbon film ribbon, the art has been working with ribbons which are cast matrices of plastic material such as nylon containing liquid ink. While such ribbon structures appear to provide the combination of high quality printing and low cost, they are highly distortable and fragile. Consequently, the ribbons can only be used for a limited number of passes, and often in a single pass printing mode, i.e., the ribbon is passed only once in its path across the printing position from the supply reel to the take-up reel.
The ribbon may conveniently be packaged in cartridges which are received by appropriate receiving means in an impact printer having means for driving the ribbon. A conventional driving means is provided by a drive belt mechanism in the printer which engages and peripherally drives the ribbon portion on one or a pair of reels mounted within the cartridge. The following copending applications assigned to the assignee of the present invention describes such ribbon cartridges and belt drives. Application Ser. No. 233, filed Jan. 2, 1979 now U.S. Pat. No. 4,264,223, issued Apr. 28, 1981, J. D. Bemis et al and Application Ser. No. 234, filed Jan. 2, 1979 now U.S. Pat. No. 4,265,552, issued May 5, 1981, J. D. Bemis et al cover a ribbon cartridge and associated peripheral drive mechanism in an impact printer wherein the cartridge is structured to permit the usage of the ribbon in two printing passes. Consequently the ribbon is printed on twice, i.e., in an initial forward and then a reverse direction, after which the ribbon cartridge is discarded. Patent Application Ser. No. 21,405, filed Mar. 19, 1979 now U.S. Pat. No. 4,264,224, issued Apr. 28, 1981, R. D. Mathews describes a ribbon cartridge which is mounted on a printer in "off-the-carrier" arrangement, i.e., the cartridge is mounted in a stationary position on the printer; it does not move along on a carrier.
Because of the relatively symmetrical external appearance of single pass ribbon cartridges containing the supply and take-up reels, an operator could very easily accidentally insert the ribbon cartridge into the impact printer receiving apparatus in such a position that the suppy reel containing the unused portion of the ribbon is inadvertently in the position which the take-up reel should occupy. This would obviously create a problem during the initial insertion of a new cartridge since the whole supply would be in the position of the already used ribbon. However, an even more significant problem would occur when a partially used ribbon cartridge would be removed during printer maintenance or for other purpose and then reinserted into the printer. In such a situation, if the already used portion of the ribbon on the take-up reel were to be inserted in the supply position in the printer cartridge receiving means, the used portion of the ribbon would be reused. This would be likely to result in printing of relatively poor quality and legibility.